In recent years, enhancement in wear resistance, wet performance, and dry performance have been demanded from the perspective of safety. The reduction in tire rolling resistance has also been demanded from the perspective of fuel efficiency when a vehicle is traveling. For these, methods of enhancing these functions by blending silica in a rubber component constituting a tread portion of a tire have been known.
However, silica has low affinity with rubber components, and the cohesiveness between silicas is high, so if silica is simply blended to the rubber component, the silica is not dispersed, which leads to the problem that the effect of enhancing these functions cannot be achieved sufficiently.
In this connection, International Patent Publication No. WO/2011/105362 discloses a rubber composition containing a conjugated diene rubber containing an isoprene block. International Patent Publication No. WO/2011/105362 describes that by using the above composition, the affinity between the silica and the rubber is good, and reduced heat build-up (low rolling resistance) and wet grip performance can be enhanced.
Meanwhile, as higher levels of safety are demanded, further enhancement in wear resistance, wet performance, and dry performance are demanded. Furthermore, environmental problems, resource problems, and the like have led to a demand for even better fuel efficiency in vehicles, which in turn has led to a demand for further enhancement in the low rolling resistance of tires.
In this connection, when the inventor of the present technology studied the rubber compositions described in International Patent Publication No. WO/2011/105362, it was found that the wear resistance, the wet performance, and the dry performance do not always satisfy the currently required levels.